1. Field of the Invention
This invention relates to an image pickup apparatus of the kind arranged to convert an object image into an electrical signal and to process the electrical signal, and more particularly to management of data stored in a memory included in the apparatus.
2. Description of the Related Art
Electronic cameras have recently been proposed and practicalized as image pickup apparatuses of the kind arranged to convert, by means of a photoelectric converting element, an object image formed by a photo-taking lens into an electrical signal and to record the electrical signal on a recording medium as an analog signal. Some electronic cameras more recently proposed are arranged to digitally store an image signal on a solid-state memory such as a memory card, a hard disk device or the like.
Generally, these electronic cameras have been arranged to perform recording immediately after a shot is taken and to permit taking another shot only after completion of recording if an instruction is given for another shot by means of a switch or the like before completion of the process of recording.
Further, in a case where a hard disk device is to be used as a recording medium, a data storing method which is contrived for use of a hard disk device as an auxiliary storage device for a computer is utilized as it is for the electronic camera. However, for image recording, this data storing method is inconvenient in the following points: In the electronic camera using the conventional digital recording method, the whole recording area of the hard disk device is divided into an information data area and a management data area. Information data is recorded in the information data area by dividing the data into units called clusters, and a state of using the information data area is recorded in the management data area.
While this recording method is convenient for recording information of varied sizes, in the event of handling only information of a fixed size such as image data, it necessitates not only an unnecessarily great amount of management work but also an excessively long period of time for recording, thereby hindering, for example, an attempt to increase the speed of continuous shooting. Further, repetitions of recording and erasure bring about fragmentation to make it impossible to record new image data in consecutive areas. This also hinders an increase in the speed of continuous shooting.
Further, it has been impossible, with the conventional electronic camera, to take any shot until the end of recording when an instruction for shooting is newly given while an image picked up by a previous shot is still in process of recording.
Digital recording methods have come to be used, as mentioned above, as a result of commercialization of large capacity digital recording media such as a hard disk device, a photoelectro-magnetic disk, flash memory, etc., and improvement in the processing capacity of computers which are arranged to be capable of copying without deteriorating picture quality.
Compared with the speed of processing a picked-up image signal, the speed of writing into a recording medium by the electronic camera is slow in general. In view of the slow writing speed, it is generally practiced to have an intermediate memory means arranged before a recording medium such as a hard disk device so as to absorb a difference between the picked-up image processing speed and the writing speed. Such an intermediate memory means may be a FIFO (first-in/first-out) memory. However, since the intermediate memory means is generally arranged to be used also for image processing actions such as compression of the image, attaining some video effect, etc., a random access memory has been popularly employed.
The speed of shooting can be enhanced by increasing the number of pictures which are simultaneously storable in the intermediate memory means. For example, in a case where the picked-up image consists of 640 horizontal picture elements and 480 vertical picture elements (lines), it is theoretically necessary to have at least 640 storage areas in the horizontal direction and at least 480.times.k (k: number of pictures storable at the same time) storage areas in the vertical direction. In order to secure more than 640 picture elements in the horizontal direction, 10 bits are necessary for horizontal addresses.
However, with the horizontal addresses assumed to have 10 bits, it becomes possible to have 1,024 picture elements in the horizontal direction. Then, storage areas for 384 picture elements would be wasted. Since this number of wasted storage areas is accumulated by the number of picture elements in the vertical direction, a considerably large part would be wastefully left unused.